1. Technical Field
The present invention generally relates to integrated circuit packaging and in particular to an improved ceramic package. Still more particularly, the present invention relates to methods for designing and fabricating ceramic packages that exhibit reduced noise coupling between signal traces and optimizes impedance discontinuity control.
2. Description of the Related Art
Crosstalk is a phenomenon by which some of the energy carried by a signal on one line/trace is transferred to a nearby line/trace. A signal net with a source of noise is called an aggressor net or an active net and the net on which the noise is generated is called the victim net or the quiet net. Crosstalk occurs because of capacitive and inductive coupling between the signal lines in electrical circuits. Crosstalk may cause noise to be generated on the adjacent quiet signal lines, which could lead to false logic switching. Crosstalk may also impact the timing on the active lines if multiple lines are switching simultaneously.
Ceramic packages have been popularly used in wide range of applications with excellent reliability and a large number of wiring capabilities. Signal speeds and the number of the signal inputs/outputs (I/Os) have increase rapidly in recent applications of ASICs; However, high noise coupling among those high speed signals has become a critical concern in ceramic packages and has severely limited the application space for ceramic packages. One mechanism for reducing noise coupling in ceramic packages proposes the use of metal fillings in mesh planes. However, this noise reduction mechanism may significantly increase the amount of metal in the layer and is limited in real ceramic package applications, which have limits for metal loading for each metal layer in ceramic packages.